• Quick retrieval from earlier learning (Reaction profiles: energy change and activation energy; Rates of reaction). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. On a reaction profile, the reactants are at 100 kJ, the peak is at 160 kJ and the products are at 40 kJ. What is the overall energy change, in kJ? (Use a minus sign if energy is released.) → -60 kJPrompt: energy change = energy of products − energy of reactants
2. A reaction produces 30 cm³ of gas in 30 seconds. What is the mean rate of reaction, in cm³/s? → 1 cm³/sPrompt: mean rate = amount of product ÷ time
3. Reactants: 140 kJ. Peak of the profile: 190 kJ. Products: 175 kJ. What is the activation energy, in kJ? → 50 kJPrompt: Activation energy is the minimum energy needed to start the reaction.

• Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
• Share the objective: Predict how an equilibrium shifts (Le Chatelier). Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. The pressure is increased. What happens to the position of equilibrium?
• Step 1: Higher pressure favours the side with fewer gas molecules.
• Step 2: So the answer is: shifts left (more reactants)
• Answer: shifts left (more reactants)
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. All substances are gases in this equilibrium: N₂O₄ ⇌ 2NO₂. The forward reaction is endothermic. More of the first reactant is added. What happens to the position of equilibrium? (shifts right (more products) / shifts left (more reactants) / no change in position) → shifts right (more products)Prompt: The system shifts to oppose the change.
2. Heating blue hydrated copper sulfate makes white anhydrous copper sulfate and water. Adding water turns it blue again. What does this show? (It is a physical change only / It is a reversible reaction / Water is a catalyst / Copper sulfate is an element) → It is a reversible reactionPrompt: It can go both ways.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. What effect does a catalyst have on the position of equilibrium? (it shifts it left / it shifts it right / none: it only helps equilibrium be reached faster / it stops the reverse reaction) → none: it only helps equilibrium be reached fasterPrompt: A catalyst speeds up both directions equally.
2. All substances are gases in this equilibrium: CO + 2H₂ ⇌ CH₃OH. The forward reaction is exothermic. The temperature is decreased. What happens to the position of equilibrium? (shifts right (more products) / shifts left (more reactants) / no change in position) → shifts right (more products)Prompt: The system shifts to oppose the change.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.